Analogs of S-adenosylhomocysteine (SAH) and S-adenosylmethionine (SAM) will be prepared and enzymatically evaluated in an attempt to elucidate the structural requirements at the active site of various methyltransferase enzymes. The enzymes of particular interest will be catechol-O-methyltransferase (COMT) and phenethanolamine-N- methyltransferase (PNMT) which are important enzymes in the biosynthesis and metabolism of biogenic amines. The structural modifications will involve the adenine moiety, specifically, the preparation of various 6-substituted-3-deazapurine analogs of SAM and SAH and the decarboxylated derivative of S-3-deazaadenosylhomocysteine and S-3-deazaadenosylmethionine. Evaluation of the SAM analogs as potential substrates or inhibitors and the SAH analogs as potential inhibitors for the enzymes COMT and PNMT will permit a more detailed delineation of the structural requirements at the active site of these enzymes.